The forms for marriage and fiance visas for the US are readily available for anyone to check:
https://travel.state.gov/content/travel/en/us-visas/immigrat...
https://travel.state.gov/content/travel/en/us-visas/immigrat...
"Throughout the process, the couples — and the noncitizens in particular — have little to no expectation of privacy. The noncitizens submit bank statements, detailed medical records (including regarding their sexual and mental health), criminal history, and biometric information."
Yes unsurprisingly a country wants to do basic background checks on people it is making permanent residents and then citizens.